Photographic relief



July 25, T TROLAND Ef' AL PHOTOGRAPHIC RELIEF Filed Sept. 4, 1931Patented 25, l193:3

UNITED STATES PATENT Y (i1-,111GE LEONARD T. 'rnoLANn AND ROLAND n.aa'r'oN, `or camminare, nssacnusm'ra assumons, BY mEsNn ASSIGNMENTS, 'ro,TEcnNIcoLoia nac., -.v ii` Naw "Yom-1N. Y.,

A coaronarroN or nELawAn-a PHOTOGBAPHIC RELIEF application mea september4, 1931. serial No. 561,137.

Photographic gelatine reliefs are mainly used for printing therefrom byimbibition methods upon elatine blanks, and according to one met od suchrelief matrices are 5 made by rendering the portions of a photographicsilver haloid emulsion, which are coextensive with a latent or develo edsilver image, insoluble in warm water, issolving the remainingr portionsand vbleaching the silver image. Matrices of'this kind, as `madeaccording tov ,previously known methods, have various-disadvantages, asfor instance an uneven ory otherwise physically irregular surface,uncontrollable irregularities' inherent in they manufacturing processwhich results in much wastage and uncertainty of output, so-calledchemical fog,N etc. Espelcially the irregular or grainyrelief surface isvery unfavorable, even if the relief is otherf 20 wise satisfactory,because the irregular protrudng surface formations, sometimes'calledprotuberances, which are mainlyinstrumental for the dye absorption andtransfer, enclose free dye between them when the matrix is pressedagainst the blank, with a resulting loss of definition. Furthermore,such a matrix transfers to the blank material a secondary dye pattern,or grain, which is.

superimposed upon the prmary or image pattern and corresponds to theprotuberance pattern of the matrix. It has not been possible with any ofthe processes for making gelatine reliefs which have been heretoforeproposed to eliminate this positive or transferee grain to a sufficientextent, for instance "for purposes of motion picture projection whichrequires a projection image fairly unbroken by grain n patterns atmagnification above fifty times the size of the positive film frame. l

Some of themain objects ofthe invention are: photographic gelatineprintingreliefs, made from silver haloid emulsions, which have apractically `smooth surface 'without protuberances or similar physicalirregularities; a process, based on fundamental-investigations vof thestructure and formation of gelatine reliefs, of making' such reliefs;

a method of controlling the actions of the 50 various lsolutions used inthis process so as to obtain the desired product with certainty and at acost not exceeding that of previously known processes. These and otherobjects will be apparent from'the following detailed explanations' ofthe genus of the invention 55 and of a commercial embodiment thereof bywsy of. example. The description refers to a rawmg 1n which:

Fig. 1gis a diagrammatic representation of a photomicrographic top viewof a'treated gelatine emulsion.; Fig'. 2 is a similar representation ofthe cross-section through a treated photographic film prior to etching;

Fig. 3ds a representation similar to Fig. 2, `after etching; and

Fig. 4 is a `representation similar to Fig. y3 of" a film l ortion oflow density. It will e'understood that these figures cantonlyfapproximately: .andV diagrammatically '10 l reproduce thecharacter of g the photomicrographs from ,which vthey have been made.-

According tothe present invention the gelatine relief matrix hasdye-absorbing portions embedded kin a relatively smooth layer of'non-absorbing gelatine above' which'these `portions do not protrude,`whereby lthe term smooth, as herein employed, re ers to sur'- facecharacteristics which influence the above mentioned secondary pattern,`but has no' relation tothe actual image pattern as reproduced bythevarying height of the relief.

A matrix having these peculiar properties is madeby employing, for thedevelo ment of a latent silver image, a so-called har ening developer,as for instance a pyrogallol or pyrocatechin developer, ,which .is freefrom reducing chemicals or substances which pro'- tect againstoxidation, as for instance sodium sulite. `Developers of this kindrender the A9o gelatine which is" coextensive with vthe .latent imagesubstantially insoluble in warm water but do not .impair its ability to'take updyes by adsorp'tiomabsforption or any otherphy'si-` cal orchemical process (hereinafter referred to as dye absorption ability).After the de'- velopment of the latent silver haloid image,

ythe film is subjected to an oxidation treatsolved air and/or to theaction of oxidizing chemicals other than water. such as potassiumferricyanide or potassium bichroinate. This treatment oxidizes thepyrogallic acid which has not been consumed in developing the image,said oxidation producing gelatine, which docs not'readily absorb dye andwhich at least partially surrounds the dye absorbent gelatineimmediately around the silver particles, resulting directly from thehardenf ing development and constitutingthe photographic image.Subsequently the emulsion is subjected to the known treatment calledetching, usually consisting in washing with water at a temperature ofabout 130 F. which removes substantially all portions of gelatine notapproximately coextensive with the silver image, that is the non-imagegelatine as distinguished from the developer hardened image gelatineproper and the image filler gelatine substantially coextensivetherewith, but of substantially the same 4 tine portions is mainly dueto the fact that apparently the filler gelatine in which the unuseddeveloper is oxidized vetches olf fairly easily although it does notabsorb dye, whereas the image part proper becomes insoluble in reactionwith the latent image constituents and readily takes up dye, which isperhaps to some degree due to the fact that these parts are renderedspongy by the removal of the developed silver grains in the bleachingprocess.

Having now generally disclosed the genus of the invention, the newmethod land the product resulting therefrom will now be described asthey have been studied in an attempt to explain their exact nature.Microscopic observation of the behaviour of pyrogallic acid inhomogeneous material, such as aqueous solutions of plain gelatine,shows' that oxidation of pyrogallie acid produces in th-e gelatinevehicle a net work of honeyy comb shape consisting of brown material,

probably some form of quinone, which does not readily take up dyes. Inthis case of homogeneous gelatine material, the size and shape of thenetwork is determined only by natural intermolecular forces. However, ifthe same experiment is made with a heterogeneous medium, as an emulsioncontaining developed silver grains, it will be seen that the network, orin the case of a very thin emulacted with the unconsu'mcdd'eveloper andythe oxidizer, would naturally surround the zones around the imageconstituents or clumps, these zones being of a different nature than thecell network, which dissolves comparatively easy in hot water but doesnot absorb dyes, whereas the image zones readily do so but resist hotwater comparatively well, which can be experimentally shown. Theproduction of the non-dye-absorbing gelatine is dependent upon thechemical action of the oxidized pyrogallic material upon the gelatinesurrounding the silver grain clumps, and it may be assumed that thisparticular structure depends upon the exhaustion of the pyrogallic acidlocally at the grain centers in consequence of development at thesepoints, thus leaving the surrounding regions moref highly impregnatedwith oxidizable substance. According to this explanation, the quantityof non-dye-absorbing but hot water soluble image ller gelatine will beapproximately inversely proportional to the quantity of dye-absorbingbut non-soluble image gelatine, so that after the non-image parts havebeen removed the non-dye-absorbing gelatine will have a tendency topredominate any regions where the photographic image is increasinglydisperse. Consequently, the relief formed in this manner will besubstantially smooth and without protuberances at all density levels,but will nevertheless vary in thickness with varying densities,representing a relief merely reproducing the image pattern without anyadditional secondary pattern.

Figs. l to 4 illustrate the various steps of the process as described.In the photomicrographic to view according to Fig. 1,H is a network oextremely non-absorbing gelatine surrounding better absorbing portionsA, whereas in the photomicrographic cross-section of a treated butunetched emulsion according to Fig. 2, the non-absorbing, nonimage, andimage filler portions are again indicated by H, S indicating the silverparticles of the image portion of the film, B being the support of theemulsion which has been exposed through this support, and A denoting thedye absorptive, insoluble portions. Fig. 3 which is also aphotomicrographic section shows the result of the etching and bleachingprocess which removes the parts not coextensive with the image, theremaining relief having dye-absorbing image parts A and non-absorptiveimage filler portions H. In regions of low densities there will besubstantially only one layer of dyeabsorbing particles, as shownin-section in Fig. 4, where 'B denotes again the base, I-I thenon-absorptive and A the non-soluble gelatine.

As shown in Fig. 3 the non-image parts of the emulsion, which consistwholly of soluble non-dye-absorbing gelatine, are entirely removed b vthe etch ;v Whereas in the image portions tlu` dye absorptive insolubleimage gelatine, which consists of pocket-like formations interconnectedby channels of the same material, remains intact, retaining within itssponge-like mesh the relatively soluble nonabsorptive image fillergelatine as far as it is coextensive with the image portion. The factthat this relatively soluble gelatine of the image portion is not etchedoff like the non-image portion of the same material can perhaps becomprehended by comparing it with a similar phenomenon which takes placeif pebbles are embedded in cement. If concrete of this sort is subjectedin a half set state to a jet of water, the cement alone does not standup at all and is washed away from the surface, laying bare the pebbles,whereas it does not permit a single pebble to be removed, so that thefinal surface appears com` parati vely smooth after all the surfacecement has been washed away, and the interstices between the pebbles arefairly well filled with cement. The analogous action of the nonetchingimage gelatine sponge is still more pronounced, so that practically nosoluble image filler gelatine is removed from between the interconnectedparticles of the non-etching gelatine sponge` leaving the relief surfacesubstantially smooth.

From the foregoing it will be seen that the ratio between the amounts ofdye-absorbing, nonetching gelatine on the one hand andnon-dye-absorbing, well etching gelatine portions on the other hand isa'n important factor in controlling the quality of the gelatine relief.If there is an excess of non-dyeabsorbing materia-l, the dye-absorbingparticles will be submerged or separated from the surface bynon-dye-absorbing material, and therefore rendered ineffective. Thisunfavorable condition is aggravated by the fact that a high degree ofoxidation, which naturally accompanies the production of laproportionally large amount of non-dye-absorbing gelatine, will renderthe latter more like the non-etching image gelatine, that is to acertain degree non-etching. In this case there will be active only asrllller number of, although perhaps (in the vgher densities) larger,dye-absorbing particles, which results in a coarse secondary pattern orgrain of the dyed relief used as such, or of transfer prints madetherefrom. With such an unfavorable ratio between the two kinds ofgelatine, there is also the danger that the lower densities arealtogether lost due to the fact that the few dye-absorbing particles ofthese densities, which may only form a single layer,

are entirely covered by `a. non-dye-absorbing layer. In lcertaincases'it is beneficialto provide so-called fog layers covering the baseinthe lower dens1ty regions, as for exam le disclosed :in United StatesPatent o. 1,677,665 to Troland and Weaver, and assignedr to theTechnicolor Motion Picture Corporation. Such foglayers are rendereduseless if the non-dye-absorbing material covers the dye-absorbingmaterial. The best condition is one in which the non-d e-absorbingmaterial is nearly, but not qulte, of the same thickness as thedye-absorbing units, so that a maximum number of dye-absorbing units,which might be compared to dye pockets, are open toward the reliefsurface and therefore able to take up and to discharge their dye andthat of the pockets connected with them by channels. This prevents thedetrimental effects of an uneven surface, as the forming of dye depositsbetween protuberances, or of water pools d uring the imbibition process,and the resultlng secondary or grain pattern of the dyed relief and/orthe transfer print.

As mentioned above the ratio of these two components can be adjusted bycontrolling the extent of oxidization after development. For instance ithas been found that by changing the pH of the washing bath thenon-dyeabsorbing material can be increased 1n amount, or heightened tosuch an extent that there is serious reduction of dye transfer in thelower and medium densities, or that the oxidizing action can bedecreased to such a degree that the relief surface becomes qulte unevenand the secondary dye pattern appears.

In carrying out the invention, the following technique has been foundsatisfactory: photographic film is exposed to a negatlve 1n any suitablemanner, and is then treated, preferably in a continuous developingmachine of suitable design, for about 31/2 minutes, at approximately 64F., in a developer of substantially the following composition:

. Percent Pyrogallic acid 0.8 Sodium hydroxide 0. 3 Ammonium chloride 0.15 Potassium bromide 0. 15 Citric acid 0.02

This developer is substantially the same as disclosed and claimed in thePatent No. 1,535.700 of Leonard T, T roland. From the developer, thefilm is removed into a wash tank, through which water is circulated insuch a manner that it is completely changed approximately once in tenminutes. The oxygen of the air contained in this water performs theoxidizing action upon which the present invention is mainly based, and avarying oxidizing capacity of the water greatly influences the qualityof the final product. It is possible to regulate and adjust thisoxidizing capacity by agitating the Water bath, or blowing a certainamount of air into it, but it has been found best to use the abovedisclosed turnover of water o f about 64 F. entering with a pH ofapproximately 6.5 (which can be attained with any suitable waterpurification system) and to keep the film for about two minutes in thisWater. lt is important to keep the pH strictly at a value best suited tothe desired gelatine relief quality, since it has been found thatvariations of the pH from about 4 to 8.vary the contrast characteristic(the socalled gamma) 0f the dyed-up relief within a comparatively widerange. As has been mentioned before, a prolonged or too vigorousoxidization is to be avoided, since it tends to make the non-imagegelatine insoluble in warm water, e. g. to render it similar in thisrespect to the non-soluble image gelatin, so that the film will notproperly etch in the subsequent warm water bath.

From the washing and oxidizing tank, the film goes for about 1% minutesinto a solution of about 14% ferricyanide in water, kept at a pH ofapproxin'iately 3.7 and a temperature of about (55 F. This ferricyanidebath oxidizes any remaining pyrogallol, acting like a developed stop,and in addition converts the developed silver into a complex, lightbrown cyanide compound, thereby bleaching the image. Furthermore, italso completely insolubilizes the dye-absorbing image gelatine.

The next step is a washing for about l/z minutes in water of a pH ofapproximately 6.5 and a telnperature of 65 F. From the washing tank, thefilm is treated for about four minutes in a fixing bath of ordinary,non-acidic sodium thiosulfate solution at approximately 650 F. whichperforms the normal fixing action and in addition removes the compoundinto which the developed silver was changed in the ferricyanide bath.

rlhe next bath is the etching bath consisting of water of about 130 F.,which dissolves the non-image portions of the emulsion. After properlydrying it, the gelatine relief can now be used either directly, bydyeing it, or as a printing matrix.

It should be understood that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

We claim: t

l. The method of controlling the dye-absorbing properties of aphotographic film which comprises treating the latent image of a silverhaloid emulsion in a hardening developing solution, oxidizing thesolution remainin; r in the gelatine, and not consumed for development`in a separate bath to a predetermined degree, thereby regulating thethickness of a layer of relatively non-dyeabsorbing gelatine produced bysaid oxidation process and filling the interstices between imageforn'iing dye-absorbent gelatine particles produced by the developingsolution, in relation to the depth ol'v the layer formed by saiddye-absorbent particles.

2. The method of making gelatine reliefs which comprises developing thelatent silver image of a photographic emulsion in a pyrogallic solution,treating the developed emulsion with a bath oxidizing the unuseddeveloper remaining inthe emulsion, and dissolving the non-imageportions of the emulsion, thereby regulating the proportion ofintermingled developed gelatine portions and gelatine portionscoextensive with said oxidized developer by varying the action of saidoxidizing bath, so that the relief surface is substantially smooth uponremoval of the nonimage portions.

3. The method of making photographic gelatine reliefs with the aid of adeveloper which renders the latent image portions of an emulsionrelatively dye-absorbing but insoluble in warm water, characterized byoxidizing the developer which remains in the image after developnwnt,thereby providing a body of relatively non-dye-absorl)ing but solublegelatine filling the spaces not oecupied by the image gelatine, so thatupon dissolution of the non-innige gelatine the remainingrelief has asubstantially smooth surface, said non-dye-absorbing gelatine beingsubstantially retained so far as intermingled with said image portions.

4. The method of making photographic gelatine reliefs which comprisesdeveloping the latent silver image of a photographie emulsion in apyrogallic solution. treating the developed emulsion with a bathoxidizing the unused developer, thereby providing a .filler layer ofrelatively non-dye-absorbing gelatine between the image portions, anddissolving the non-image portions, whereby said filler layer issubstantially protected against dissolution, by said image portions.

5. The method of making photograph gelatine reliefs which comprisesdeveloping the latent silver image of a photographic emulsion in apyrogallic solution,- treating the emulsion in a hath partiallyoxidizing the pyrogallic solution not consuned for development, wherebya filler layer of relatively non-dye-absorbing gelatine remains betweenthe image forming dye-absorbent gelatine portions produced by thedeveloping solution, and dissolving the non-image portions. whereby saidfiller layer is substantially pro-r tected against dissolution, b v saidimage portions.

6. The method of making photographie gelatine reliefs which comprisesdeveloping the latent image of a silver haloid emulsion in an alkalinepyrogallic solution, treating the emulsion in an aerated water bathoxidizing the pyrogallic solution not consumed for development, andremoving the gelatine substantially not coextensive with the developedimage portions, whereby a filler layer of relatively non-dye-absorbinggelatine remains between the image forming dye-absorbent gelatineparticles produced by the developing solution.

7. The method of making photographic gelatine reliefs which comprisesdeveloping a silver haloid emulsion containing a latent image in analkaline pyrogallic solution, treating the emulsion in a bath capable ofoxidizing the pyrogallic solution not consumed for development, andremoving the gelatine substantially not coextensive with the developedimage portions, whereby a filler layer of relatively non-dye-absorbingbut relatively soluble gelatine remains between the image formingrelatively dye-absorbent but insoluble gelatine particles produced bythe developing solution.y both gelatine constituents conjointlyestablishing a substantially smooth relief surface.

gelatine, the surface of said relief being substantially smooth.

10. A photographic gelatine relief comprising image formingdye-absorbing gelatine particles substantially insoluble in warm water,embedded in relatively non-dye-absorbing, relatively soluble gelatine,said soluble portion forming upon the relief surface fillets connectingthe image forming gelatine particles.

LEONARD T. TROLAND. ROLAND D. EATON.

